This invention relates to an improved apparatus that rinses chemicals from semiconductor wafers and then dries the wafers using an inert heated gas. The apparatus utilizes a spin process for both the rinse and dry cycles.
The process of manufacturing integrated circuit (IC) chips consists of coating, etching and cleaning semiconductor wafers which later in the process are carefully cut into small chips or die. One of the critical steps in this process is the cleaning process which follows chemical etching. The cleaning process includes loading the wafers into a wafer carrier, placing the wafer carrier in a spin rinser/dryer, rinsing the wafers in deionized (DI) water while spinning, and drying the wafers by passing an inert heated gas over the wafers while still spinning. The cleanliness of the water can be monitored during the rinse cycle by a resistivity measuring means that interlocks the rinser/dryer so that it does not go into a dry cycle until the water reaches a predetermined resistivity, indicating a proper water cleanliness. The wafer manufacturing and cleaning processes are generally carried out in cleanrooms which often exceed the cleanliness requirements of a hospital operating room. This super cleanliness insures that wafers do not become contaminated by particulate matter. Consequently, great emphasis is placed on using dust free materials and maintaining a dust free environment. Careful attention is paid to ventilation systems in order to minimize contaminating this clean environment.
U.S. Pat. No. 4,300,581 issued Nov. 17, 1981 discloses an automatic centrifugal wafer processor. The processor features include an inclined stainless steel tub, an automatic rinse termination timer, a liquid conductivity monitoring means, a wafer support device, a drive motor and a glass viewing window in the front opening door. This type of commercially available processor, although adequate for the applicant's needs is characterized by a number of problems namely:
1. The shape of the outer front housing has sharp bends that create turbulence in a down flow air ventilation system typical in a cleanroom. Turbulent air in a cleanroom is undesirable since it stirs up any dust that may be present.
2. The outer housing does not provide an easy access to interior controls, valves, motor, and bearings for maintenance.
3. The outer housing shape does not lend itself to placing the front of the processor in a cleanroom and the back of the unit behind a walled corridor, or plenum (maintenance area), not necessarily a clean area.
4. Maintenance on the apparatus is difficult by virtue of the housing construction and the rotating tub being mounted on four shock mounts.
5. Although not shown in U.S. Pat. No. 4,300,581, the plumbing fixtures, including nitrogen supply, water supply, and water drain piping all are supported from the back of the machine and have to be dismantled prior to performing any maintenance on the machine internal devices.
6. One hand must be free in order to open the door or start the machine by actuating the push button. This restricts the operator from carrying more than one wafer support carrier unless one of the carriers is set down.
7. The wafer support device (that holds the wafers in their respective slots in the carrier), consists of a plastic coated bent steel rod, that attaches to a support ring on the front and a rotor on the back. If the plastic coating is damaged, the entire rotor, support ring, etc. has to be removed in order to undo the bent steel rod fastener at the back of the rotor and then replace the damaged plastic coating.
8. The single alarm point resistivity monitor can give a false high reading, indicating clean water in the case when there is no water surrounding the probe, i.e., the monitor probe is in air.
9. The bowl drain has a square cross-section causing difficult cleaning of the square edges during maintenance periods.
10. Although not specifically shown or stated in the prior art figures, the drive motors have typically been a brush type D.C. motor since the required variable speeds are most easily accomplished by D.C. motors. One of the problems created by theses D.C. motors is generation of carbon dust as the brushes wear on the commutator. Carbon dust in the clean area creates a contamination hazard for the process.
11. A subsequent later version of the wafer processor contains a rotor quick disconnect device that has failed. This device disconnected the rotor from an in-line motor shaft by means of an expansion ring that contracted and expanded within the motor shaft. A failure of the disconnect device during operation causes internal damage to the carousel and stainless steel bowl.
It is the purpose of this invention to correct the problems identified above by an apparatus that has a unique housing, improved maintenance accessibility to internal parts from a non-cleanroom plenum, improved wafer carrier holders (carousels), foot-operated switches for the door, a means for monitoring water cleanliness that identifies a lack of water, and an improved quick disconnect rotor means.